The subject of the invention is a filler is a filler of the glassy type for plastics and resins and a process for obtaining it.
As known,  less than  less than fillers greater than  greater than  are of great importance in the overall composition of articles and products based on resins, especially phenolic resins, and on plastics, especially when these articles and products are produced by a molding operation.
Fillers are an additive material which is normally incorporated into the polymers and can fulfil, depending on the situation, the function of simply filling the polymer or that of significantly reinforcing it.
As a percentage by weight, the amount of fillers may even be very high, for example 40%, and they can have a key influence on the physicochemical characteristics of the articles produced.
Among the various existing fillers, those of the glassy type are very important and very widely used, and one well-known type of glassy filler consists of minute, approximately spherical, glass elements hereafter called microspheres or granules, the maximum diameter of which is very small, for example about one tenth or one hundredth of a millimeter.
The polymers or  less than  less than matrices greater than  greater than  which surround these glass microspheres or granules result in articles whose abrasion resistance, impact strength, compressive strength and flexural strength are improved and which exhibit impermeability and enhanced acid and solvent resistance.
Further advantages resulting from the use of said glass microspheres or granules as fillers are the overall improvement in the electrical and thermal properties.
The molding operations are markedly improved because of the reduction in the in-mold shrinkage and a smoother and better finished molding surface is obtained.
There is also as a result a cost reduction in proportion to the cost and amount of microspheres added.
Unfortunately, these glass microspheres cannot be simply added to said materials or matrices made of plastic or phenolic resins.
This is because they require to be pretreated on the surface with substances, called  less than  less than sizing compositions greater than  greater than , which act as a binder between the glass and the matrices in order to guarantee perfect and lasting adhesion to the glass. Among sizing compositions recognized as being the most effective are those commonly called  less than  less than silanes greater than  greater than . These particular sizing compositions consist of molecules having one part provided with affinity for the glass of the microspheres and another part capable of copolymerizing with the matrices.
In practice, said microspheres or granules are basically made of glass coated with an appropriate-type sizing composition.
The abovementioned known technique obviously has advantages and disadvantages. As already mentioned, the advantages relate to the qualitative improvement to the end-products which contain said microspheres. The drawbacks stem from a certain difficulty in the production of said microspheres and from their cost.
This is because they must have well-defined dimensions. In particular, the glass particles which form them must have small dimensions, between one tenth and one hundredth of a millimeter. In order to produce such particles, very expensive systems and equipment must be used.
Furthermore, the subsequent application of the sizing compositions introduces an additional phase which adds to the production phase of the glass part, with a substantial cost increase.
The high production cost and application cost of sizing compositions consequently mean an increase in the cost of the end-products and considerably reduce the use of the fillers described.
In fact, it should not be forgotten that the fillers used in plastics are often regarded as a filling which makes it possible to reduce, in a simple and effective manner, the overall costs of the materials employed in the molding operations.
Another disadvantage stems from the fact that, despite the use of sizing compositions, the bonding of the microspheres or granules to the matrices is not always optimal. From this standpoint, it is certainly desirable to obtain better adhesion between the glass and the polymer.
The technical objective of the invention is therefore to substantially reduce the abovementioned disadvantages, particularly those associated with the cost and the process for manufacturing said micro-spheres or granules, and with the bondability of these microspheres or granules to the matrices which surround them.
This objective is achieved by the present invention which provides a glassy-type filler for plastics and resins, especially phenolic resins, the glassy filer comprising granules of glassy material which are provided with a sizing composition, wherein each of said granules comprises a multiplicity of fragments of glassy material agglomerated together by said sizing composition.
In the context of the present invention, the term xe2x80x9csizing compositionxe2x80x9d refers to compositions which act as a binder between the glass and the matrices in order to guarantee perfect and lasting adhesion to the glass. Among sizing compositions recognized as being the most effective are those commonly called xe2x80x9csilanesxe2x80x9d. These particular sizing compositions consist of molecules having one part provided with affinity for the glass or the microspheres and another part capable of copolymerizing with the matrices.
According to advantageous characteristics:
said sizing composition comprises a compound chosen from esters of alkylsilicic acids;
said sizing is an aminosilane, in particular of formula NH2xe2x80x94Rxe2x80x2xe2x80x94Si(OR)3, in which:
Rxe2x80x2 denotes an optionally substituted, saturated or unsaturated, linear or branched hydrocarbon chain advantageously containing from 1 to 20 carbon atoms, especially from 2 to 8 carbon atoms, preferably an alkylene chain;
R denotes an alkyl group, preferably having from 1 to 5 carbon atoms.
One particularly preferred silane is amino-propyltriethoxysilane NH2(CH2)3Si(OC2H5)3;
said granules have a maximum mean size of between twenty and sixty micrometers and comprise at least two of said fragments;
said fragments have on average a maximum linear dimension of between five and fifteen micrometers;
said fragments are made of glass, especially  less than  less than E greater than  greater than -type glass;
said fragments are made of milled glass;
said fragments are portions of glass yarns;
the amount of said sizing composition is substantially between five and fifty parts per thousand parts, especially between five and twenty-five parts per thousand parts, by weight of the dry glassy material;
the sizing composition furthermore contains a mineral binder, such as a clay or a mixture of clays.
The subject of the invention is also a process for obtaining this filler, characterized in that it comprises: a milling step in which the glassy material is reduced to fragments; a metering step in which a mixture including said fragments and a sizing composition is formed; and an agglomeration step in which said mixture of fragments and sizing composition is dried so as to form compact granules each including a multiplicity of said fragments and of the portions of said dried sizing composition.
According to advantageous characteristics:
said milling step is preceded by a selection step in which glass yarns coming from production waste and scrap are chosen for said milling step;
said milling step is extended until fragments are obtained which have on average a maximum linear dimension of between five and fifteen micrometers;
during said milling step, water and a plasticizer and/or a mineral binder such as a clay, for example bentonite, are added to the glassy material;
during said metering step, said fragments are mixed with a sizing chosen from esters of alkylsilicic acids, especially an aminosilane;
during said metering step, said sizing composition is metered in an amount of between five and fifty parts per thousand parts by weight of dry glassy material;
during said agglomeration step, said mixture of fragments and sizing composition is heated to a drying temperature of between one hundred and twenty-five and one hundred and forty-five degrees Celsius;
said agglomeration step is carried out in a heated vessel and said mixture of fragments and sizing composition is injected into said vessel by means of compressed air so as to form granules having on average a maximum size of between twenty and sixty